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An Examination of Speech Recognition in a Modulated Background and of Forward Masking in Younger and Older Listeners

Contact author: René H. Gifford, who is now at the Mayo Clinic, Department of Otorhinolaryngology, Eisenberg 2F, 200 First Street S.W., Rochester, MN 55905. E-mail: gifford.rene{at}mayo.edu.

Purpose: To compare speech intelligibility in the presence of a 10-Hz square-wave noise masker in younger and older listeners and to relate performance to recovery from forward masking.

Method: The signal-to-noise ratio required to achieve 50% sentence identification in the presence of a 10-Hz square-wave noise masker was obtained for each of the 8 younger/older listener pairs. Listeners were matched according to their quiet thresholds for frequencies from 600 to 4800 Hz in octave steps. Forward masking was also measured in 2 younger/older threshold-matched groups for signal delays of 2–40 ms.

Results: Older listeners typically required a significantly higher signal-to-noise ratio than younger listeners to achieve 50% correct sentence recognition. This effect may be understood in terms of increased forward-masked thresholds throughout the range of signal delays corresponding to the silent intervals in the modulated noise (e.g., <50 ms).

Conclusions: Significant differences were observed between older and younger listeners on measures of both speech intelligibility in a modulated background and forward masking over a range of signal delays (0–40 ms). Age-related susceptibility to forward masking at relatively short delays may reflect a deficit in processing at a fairly central level (e.g., broader temporal windows or less efficient processing).

KEY WORDS: forward masking, effects of age, modulated noise, speech recognition

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